The purpose of this study is to investigate the clinical usefulness of a long-acting somatostatin analogue (SMS 201-995) in controlling the signs and symptoms of hormone secretion by tumors. Patients who respond are offered long-term treatment and the effects of the analogue on clinical and biochemical tumor behavior is assessed. Of the patients who have been controlled to date, 70% of patients with acromegaly have developed gallbladder sludge and 20% have developed gallstones, and two patients with TSH secreting tumors have developed gallstones. Patients currently enrolled who have persistent sludge or stones will be treated in an open- label trial with ursodeoxycholate. New patients to the study will enter a randomized, placebo controlled trial of ursodeoxycholate (or placebo) plus SMS 201-995, to determine whether sludge and stone formation can be prevented. Ultrasound examinations of the gallbladder will be performed at baseline, 4-6 weeks, 3 months, and 6 months of the trial. If the agent proves useful for preventing sludge formation, we will offer patients continued treatment with ursodeoxycholate in an open-label trial for up to two years.